Diffuser with boundary layer removal

ABSTRACT

A diffuser for a radial flow compressor has a body defining radially and tangentially extending diffusing passages from near the compressor rotor into a plenum surrounding the diffuser body. A curved diverging outlet tube is mounted in a socket at the outer end of each diffusing passage. A slot extending around the diffusing passage at the inner end of each outlet tube receives boundary layer air from the passage and directs it into a recess on the exterior of the outlet tube. All these recesses are connected to a common manifold from which the boundary layer air is directed to any suitable receiver.

United States Patent v 1191 Langham Dec. 24, 1974 [54] DIFFUSER WITH BOUNDARY LAYER 3,768,919 10 1973 OConnor 415 010. 1

REMOVAL FOREIGN PATENTS OR APPLlCATlONS [75] Inventor: Stephen Langham, Indianapolis,1nd. 1,043,168 9/1966 Great Britain 415/D1G. 1

A lM I [73] sslgnee Geller-a Ptors corporanon Primary ExaminerHenry F. Raduazo Detroit, M1ch.

Attorney, Agent, or FlrmPaul Fitzpatrick [22] Filed: July 27, 1973 [21] Appl. No.: 383,329 ABSTRACT A diffuser for a radial flow compressor has a body de- [52] US. Cl 5/207, 115/21 1 HS/DIG l fining rad1ally and tangentially extending dlffusmg pas- [511 Int Cl F0 29/44 sages from near the compressor rotor mto a plenum Surrounding the diffuser body A Curved diverging [58] Fleld of Search 4l5/DIG. 1, 207, 211,181, 1 b d k t th t d f 60/3951 39 417/409 et tu e 1s mounte in a soc e at eou er en 0 each diffusmg passage. A slot extendmg around the [56] References Cited diffusmg passage at the mner end of each outlet tube receives boundary layer air from the passage and d1 UNITED STATES PATENTS rects it into a recess on the exterior of the outlet tube. 2,084,463 6/1937 Stalker 415/D1G. 1 All these recesses are connected to a common mani- 23356996 10953 Schwartlm fold from which the boundary layer air is directed to 2,709,917 6/1955 Bruynes any Suitable receiver 3,333,762 8/1967 Vrana 3,420,435 l/1969 Jarosz et al. 415 211 4 Claims, 2 Drawing Figures DIFFUSER WITH BOUNDARY LAYER REMOVAL My invention relates to diffusers for centrifugal compressors and particularly to an improved structure for removing stagnant boundary layer air from the walls defining the diffusing passages of such diffusers. The invention also is directed to an arrangement for directing the outflow from a centrifugal compressor with greater radial and smaller tangential components of velocity than is customary.

It may be desirable to remove the air flowing along the walls bounding the diffusing passages of a centrifugal compressor diffuser to improve flow conditions and also to make such air available for pressurizing seals in an engine in which the compressor is included, for cooling purposes, or for any other use to which air bled from the compressor may be put. It is highly advantageous, if air is to be bled, to take it from the boundary layer air which is relatively slow moving and if allowed to accumulate sufficiently may tend to flow reversely rather than toward the outlet of the diffuser.

Also, in certain regenerative engines the high degree of swirl around the axis of the compressor of air discharged from a conventional diffuser tends to promote an unbalanced distribution of flow over the area of regenerator matrices which are provided to heat the air delivered by the compressor. For this reason, my invention includes also in its preferred embodiment curved tubes terminating the diffusing passages which curve away from the surface of the diffuser body so as to direct the air more nearly radially than would otherwise be the case.

By way of background. it may be pointed out that my diffuser may be incorporated in an engine generally of the type shown in patents to Amann et al., U.S. Pat. No. 3,116,605, Jan. 7, 1964, and to Bell, U.S. Pat. No. 3,680,983, Aug. 1, 1972.

1 am aware that removal of boundary layer air from centrifugal compressor diffusers has been previously proposed as, for example, in U.S. Pat. No. 2,656,096 to Schwarz, Oct. 20, 1953. FIG. 9 of the patent discloses removal of boundary layer air and supply of the air to a turbine of a gas turbine engine. I am also aware of disclosures of compressor diffusers including outlet tubes of one sort or another incorporated into the diffusers in Vrana U.S. Pat. No. 3,333,762, Aug. 1, 1967, and Jams: et al., U.S. Pat. No. 3,420,435, Jan. 7, 1969.

However, it will be seen from the detailed description of the preferred embodiment that a diffuser according to my invention incorporates advantageous structure which, as far as I am aware, is new in the art.

The principal object of my invention is to improve the operation of compressor diffusers. A further object is to provide for more nearly radial outflow from compressor diffusers. A further object is to provide improved structure for bleeding of boundary layer air from a compressor diffuser.

The nature of my invention and the way in which these objects are accomplished will be clear to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention with reference to the accompanying drawings.

FIG. 1 is a partial sectional view of a centrifugal compressor taken in a plane containing the axis of rotation of the compressor.

FIG. 2 is an enlarged sectional view, taken in a plane at right angles to the axis of rotation, as indicated by the line 2-2 in FIG. 1.

The drawings illustrate a compressor for compressing a gaseous medium, one which is specifically for compressing air. The medium will be referred to hereinafter as air, although it should be understood that it may be any other gaseous medium. The compressor 2 is of the radial flow type comprising an impeller 3 having a hub or disk 4. An annular array of blades 6 extend from the disk. The impeller is mounted in bearings (not illustrated) for rotation about an axis contained in the plane of FIG. 1. Rotation of the impeller draws air into an annular air entrance 7. The air is discharged from the periphery of the impeller at 8 with a considerable radial component of velocity and a greater tangential component. The impeller is rotating clockwise as shown in FIG. 2 and is upper margin is rotating away from the plane of the view in FIG. 1. The impeller may follow known or usual practice and may, for example, be as described in Atkinson U.S. Pat. No. 2,819,012, Jan. 7, 1958. The impeller is mounted between a rear plate 10 and a front plate 11. The rear plate supports a bearing for the shaft (not illustrated) on which the rotor is mounted and mounts a seal ring 12 which cooperates with a labyrinth seal ring 14 on the rotor shaft. The air entrance 7 is defined between the forwardly extending central portion of the front plate 11 and the rotor hub. The plates 10 and 11 are fixed together by suitable means such as a ring of bolts 13 and define between their outer portions a plenum chamber 15 to which the air is directed from the impeller 3, and from which it flows to a device such, for example, as'the combustion apparatus of a gas turbine engine. In the specific environment for which my diffuser is intended, the air flows through a regenerator disk to which the air is directed from plenum 15.

The air discharged by the impeller 3 flows through passages in a diffuser body 16 in the form of an annular disk which is clamped or otherwise secured between the front and rear plates. The body 16 defines radially and tangentially extending diffusing passages 18 which extend from the cylindrical inner margin 19 of the diffuser body nearly to its outer margin. These passages may be of the nature of those shown in the Vrana patent referred to above or in an application of Phiroze Bandukwalla, Ser. No. 229,408, filed Feb. 25, 1972, [U.S. Pat. No. 3,778,186]. The passages 18 intersect at the inner boundary of the diffuser and extend with straight or curved centerlines radially and tangentially toward the outer surface. These passages may be formed by precision casting or otherwise. They diverge (at least the downstream portions of the passages diverge) to reduce the velocity of the air discharged from the impeller and convert kinetic energy into pressure.

As shown more clearly in FIG. 2, each passage 18 terminates in a preferably cylindrical socket 20 in which is mounted a diffuser outlet tube 22 which continues the diverging diffusing passage to a final outlet 24. In the preferred embodiment of the invention, the tubes 22 have a curved centerline so as to direct the flow in a more radial and less tangential direction than would be the case if'they followed the centerlines of passages 18.

Each tube 22 has an entrance 23 having substantially the same diameter and cross section as the terminus of the diffusing passage 18. Each outlet tube includes a mounting portion 26 of preferably cylindrical outline having two circumferential grooves or recesses 27 and 28 extending around its outer surface. The mounting portions fit within the socket and the tube is secured in the socket by brazing or otherwise. For brazing purposes, a wire of braze material may be located in the groove 28. The mounting portion 26 has an annular recess at its inner end to define an exit slot 30 extending around the diffusing passage. This exit slot is connected to the recess 27 by four grooves 31 extending across the inner end of the outlet tube and up the outer surface to intersect recess 27.

Boundary layer air flowing slowly along the wall defining the passage 18 may enter the exit slot 30 and flow thence into the recess 27. From this recess, the air is discharged through a port 32 opposite each outlet tube into a manifold 34 defined by a recess extending around the forward face of the diffuser l6 and by the rear face of front plate 11. The boundary layer air is allowed to flow from, or is drawn off from, the manifold 34 through a passage 35 drilled or otherwise formed in front plate 11. A discharge pipe 36 may be suitably connected to the front plate so that flow may proceed from all of the exit slots 30 through recesses 27, ports 32, manifold 34, passage 35, and pipe 36 to any suitable point of use which may, for example, be a pressurized seal in the engine or cooling fluid inlet to the turbine which drives the compressor.

My invention is not concerned with the utilization of the removed boundary layer air. It may be pumped out or may flow out under its own pressure.

As will be apparent, the inlet tubes 22 turn the flowing air through a considerable angle so that it loses a large part of its swirl velocity and may exhaust from the diffuser substantially in a radial direction. The purpose of this is to prevent the swirl velocity of the air from 10 surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket, each tube diverging downstream and having a curved centerline directed to turn the flow into a more radial direction; the diffuser defining a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; meens defining a manifold extending circumferentially of the diffuser; and means within the 20 body defining passages connecting the exit slots to the manifold.

3. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket, the diffuser defining a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; each outlet tube having a circumferential recess connected to the exit slot; and means defining a manifold extending circumferentially of the diffuser defined creating unequal distribution of air through the outlet in part by a recess in the side face of the body; the body from plenum 15 to the regenerator of the engine or other structure to which the air is directed.

It should be apparent from the foregoing that l have devised a very simple and effective structure for improving the performance of centrifugal compressors and providing for drawing off boundary layer air.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

I claim:

1. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket; the diffuser body defining a boundary layer exit slot between the radially inner end defining ports connecting the outlet tube recesses to the manifold.

4. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body 40 defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket, each tube diverging downstream and having a curved centerline directed to turn the flow into a more radial direction; the diffuser defining a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; each outlet tube having a circumfertube recesses to the manifold. 

1. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket; the diffuser body defining a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; means defining a manifold extending circumferentially of the diffuser; and means within the body defining passages connecting the exit slots to the manifold.
 2. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket, each tube diverging downstream and having a curved centerline directed to turn the flow into a more radial direction; the diffuser definIng a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; meens defining a manifold extending circumferentially of the diffuser; and means within the body defining passages connecting the exit slots to the manifold.
 3. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket, the diffuser defining a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; each outlet tube having a circumferential recess connected to the exit slot; and means defining a manifold extending circumferentially of the diffuser defined in part by a recess in the side face of the body; the body defining ports connecting the outlet tube recesses to the manifold.
 4. A diffuser for a centrifugal compressor comprising, in combination, a generally annular diffuser body defining diverging diffusing passages extending generally radially and tangentially from the radially inner surface of the body to the radially exterior surface of the body, the radially outer end of each passage being enlarged to provide a socket; a diffuser outlet tube mounted in each socket, each tube diverging downstream and having a curved centerline directed to turn the flow into a more radial direction; the diffuser defining a boundary layer exit slot between the radially inner end of each outlet tube and the bottom of the corresponding socket; each outlet tube having a circumferential recess connected to the exit slot; and means defining a manifold extending circumferentially of the diffuser defined in part by a recess in the side face of the body; the body defining ports connecting the outlet tube recesses to the manifold. 